Effect of Field Variability in Soil Hydraulic Properties on Solutions of Unsaturated Water and Salt Flows

Abstract

AbstractUsing actual field variability data and the stochastic approach, effects of spatial variability of soil hydraulic properties on the predictions of water and salt flow distributions, and of correlation structure, are evaluated. The governing water and salt flow equations are solved numerically using actual field data of soil hydraulic conductivity and differential water capacity. These data, which had been obtained previously from measurements made in 30 different locations in a field, were the same as those obtained from a Monte‐Carlo simulation that considered the correlations between the parameters of the hydraulic functions. Simulated values of pressure head (h), water fluxes (q), wetting front positions (Zf), and solute concentration (c) for each of the 30 locations in the field were used to estimate distribution types (normal or log‐normal) and its moments, for h, q, Zf, and c. The two‐point autocorrelation functions of pressure head, wetting front, and solute concentration have been calculated and used to estimate the integral scales of h, Zf, and c. Distances in the field in which the horizontal flow components were negligibly small compared with the vertical flow components were calculated and found to be in the order of 10 cm and larger. Field dispersion of solutes was calculated from the simulated salt distribution results. Values of field scale dispersivity were estimated to be larger than the pore scale dispersivity and to increase with soil depth. An “equivalent” uniform porous medium, which was defined at the soil surface, exists for large infiltration time when a unit hydraulic gradient may be assumed.